Composition for positive type photoresist

ABSTRACT

A photoresist composition including a polymer resin for forming a photoresist layer, a photosensitive chemical that changes the solubility of the photoresist layer when exposed to some form of radiation and 3-methoxybutyl acetate and 4-butyrolactone as a solvent, is provided. The composition has a good photosensitivity and remainder ratio and no unpleasant odor.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a composition for a positive typephotoresist for manufacturing fine circuit patterns such as liquidcrystal display circuits or semiconductor integrated circuits and, moreparticularly, to a composition for a positive type photoresist,including polymer resin, that produces a photoresist layer,photosensitive chemical, and solvents without unpleasant odor.

(b) Description of the Related Art

For producing fine circuit patterns such as those used in liquid crystaldisplay (LCD) circuits or semiconductor integrated circuits, aphotoresist composition is uniformly coated or applied on an insulatorlayer or a conductive metal layer on a substrate. The coated or appliedsubstrate is then exposed through a mask to some form of radiation, suchas ultraviolet light, electrons, or X-rays. And the exposed substrate isdeveloped to produce a desired pattern. The patterned photoresist filmis used as a mask to remove the insulator layer or the conductive metallayer. The remaining photoresist layer is removed to complete the finepattern onto the substrate surface. Photoresist compositions areclassified into negative and positive types depending on whether theexposed areas of photoresist coating become insoluble or soluble.Recently, positive type photoresist compositions have been preferredbecause the positive type photoresists can form smaller patterns thanthe negative type photoresists.

The important properties of photoresist compositions for commercial useare photosensitivities, contrast, resolution, adhesivity to thesubstrate, remainder ratio and safety.

Photosensitivity refers to the speed how fast the photoresist respondsto light. Higher photosensitivity is required, particularly inapplications where a number of exposures are performed to form multiplepatterns by a repeated process. The other examples are when reducedlight is used, like the projection exposure techniques that use lightpassed through a series of lenses and mono-chromatic filters.

Contrast refers to a ratio between the percentage of film loss in theexposed development area and the percentage of film loss on theunexposed area. Ordinarily, development of an exposed resist coatedsubstrate is continued until the coating on the exposed area iscompletely dissolved away. Thus, development contrast can be determinedsimply by measuring the percentage of the film coating loss in theunexposed areas when the exposed coating areas are removed entirely.

Resolution refers to the capability of a photoresist composition howfinely to reproduce the mask image utilized during exposure on thedeveloped exposed spaces. In many industrial applications, particularlyin the manufacture of LCDs or semiconductor integrated circuits, aphotoresist is required to provide a high degree of resolution for veryfine line and space widths of 1 μ or less.

Generally, photoresist composition includes a polymer resin forproducing a photoresist layer, photosensitive chemicals, and a solvent.Various attempts have been made previously to improve thephotosensitivity, contrast, resolution, and the safety of positivephotoresist compositions. For example, U.S. Pat. No. 3,666,473 disclosesthe compound of a mixture of two phenol formaldehyde novolak resinstogether with a typical photosensitive chemical. U.S. Pat. No. 4,115,128discloses that an organic acid cyclic anhydride was added to thephenolic resin and naphthoquinone diazide photosensitive chemical toincrease photosensitivity. U.S. Pat. No. 4,555,069 discloses thatnovolak resin and o-quninone diazide photosensitivity chemical andpropylene glycol alkyl ether acetate solvent are used for higherphotosensitivity and for increased safety.

Various solvents have been developed to improve physical properties ofthe photoresist composition and work safety. For example, ethyleneglycol mono ethyl ether acetate or ethyl lactate, propylene glycol monoethyl ether acetate may be used as solvent. However, the photoresistcomposition including ethyl lactate exhibits poor adhesivity to thesubstrate and it is difficult to be uniformly coated on a substrate.Ethylene glycol mono ethyl ether acetate or propylene glycol mono ethylether acetate is toxic and generates an unpleasant odor. Accordingly,there is still a need for photoresist compositions that are suitable forvarious industrial applications, without sacrificing any one of theproperties of photosensitivity, contrast, resolution, or solubility ofpolymer resin.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a composition for apositive type photoresist that exhibits high photosensitivity, remainderratio, contrast, resolution, and substrate adhesivity for varieties ofindustrial applications.

It is another object to provide a composition for a positive typephotoresist that is safe, without unpleasant odor, and environmentallyfriendly.

These and other objects may be achieved by a composition for positivetype photoresist of the present invention. This composition includes apolymer resin for forming a photoresist layer, a photosensitive chemicalthat changes solubility of the photoresist layer when exposed to someform of radiation, and a solvent of 3-methoxybutyl acetate and4-butyrolactone. The polymer resin is preferably a novolak resin and thephotosensitive chemical is preferably a diazide-type compound. The ratioof 3-methoxybutylacetate:4-butyrolactone is 60 to 80 parts by weight3-methoxybutylacetate to 2 to 10 parts by weight 4-butyrolactone.

DETAILED DESCRIPTION OF THE INVENTION

The useful polymer resins employed in a photoresist composition of thepresent invention are well known in the related arts. A novolak resin,an exemplary polymer resin, may be employed in a photoresist compositionof the present invention. The novolak resin is produced by reactingaromatic alcohol such as phenol, meta and/or para cresol withformaldehyde. To improve the photoresist, the molecular weight of theresin may be controlled by adjusting the ratio among high, medium or lowmolecular resins depending on the purpose of the photoresist.

The useful diazide compound for a photosensitive chemical may beproduced by reacting polyhydroxy benzophenone with a diazide-basedcompound such as 1,2-naphtoquinonediazide, or2-diazide-1-naphtol-5-sulfonic acid.

The solvent includes 3-methoxybutyl acetate and 4-butyrolactone. Theratio of 3-methoxybutyl acetate:4-butyrolactone is preferably 60 to 80parts by weight 3-methoxybutyl acetate to 2 to 10 parts by weight4-butyrolactone, and more preferably 65 to 75 parts by weight3-methoxybutyl acetate to 2 to 5 parts by weight 4-butyrolactone.

3-methoxybutyl acetate exceeding the above range decreases the viscosityof the composition and renders the remainder ratio poor. On the otherhand, 3-methoxybutyl acetate less than the above range increases theviscosity too much such that the ability to coat becomes poor.4-butyrolactone exceeding the above range reduces the remainder ratio.On the other hand, 4-butyrolactone less than the above range may causeproblems in obtaining the homogeneous composition and particles mayeasily occur on the substrate.

In the present invention, the photoresist composition includespreferably about 10 to about 25 wt. % of the polymer resin, about 4 to10 wt. % of the photosensitive chemical, and 65 to 85 wt. % of thesolvent.

If the amount of the polymer resin is less than 10 wt. %, the adhesionto substrate is reduced and the produced profile becomes bad. On theother hand, if the amount thereof is more than 25 wt. %, the increasedviscosity reduces the photosensitivity and the ability to coat thecomposition. If the amount of the photosensitive chemical is less than 4wt. %, the resolution is reduced and the profile becomes bad. However,more than 10 wt. % of photosensitive chemical easily produces scum orparticles in coating the photoresist composition on the substrate.

Additives such as a colorants, dyes, anti-striation agents,plasticizers, adhesion promoters, speed enhancers, and/or surfactantsmay be added to the photoresist composition of the present invention.Such additives help to improve the performance of the photoresistcomposition.

The photoresist composition of the present invention can be applied to asubstrate by such conventional method as dipping, spraying, whirling andspin coating. When spin coating, for example, the photoresist solutioncan be adjusted in respect to the percentage of solid contents in orderto provide a coating of the desired thickness given the type of spinningequipment utilized and the spinning process. Suitable substrates includesilicon, aluminum, silicon dioxide, doped silicon dioxide, siliconnitride, tantalum, copper, polysilicon, ceramics, and aluminum/coppermixtures or polymeric resins.

The substrate coated with photoresist composition is heated at 20° C. to100° C. to perform soft-baking. This step permits the evaporation of thesolvent without pyrolysis of a solid component in the photoresistcomposition. Generally, the concentration of the solvent is preferablyreduced to minimum by the soft-baking step, and thus, the soft-bakingstep is performed until the solvent is mostly evaporated and a thincoating layer of photoresist remains on the substrate.

Next, the substrate coated with the photoresist layer is selectivelyexposed to light, particularly, ultraviolet light using a suitable maskto obtain a desirable pattern. The exposed substrate is then dipped intoan aqueous alkaline developing solution until either the exposedphotoresist layer is all or almost entirely dissolved. Suitable aqueousdeveloping solution includes an aqueous solution including alkalinehydroxides, ammonium hydroxide, or tetramethylammonium hydroxide (TMAH).

The substrate with the exposed photoresist removed is then taken outfrom the developing solution. The resulting substrate is heat-treated toimprove and to increase the chemical resistance of the photoresistlayer. The step is called a hard-baking step. The hard-baking is done ata temperature below the softening point of the photoresist layer,preferably at about 100° C. to 150° C.

The developed substrate is treated with an etchant or with vapor plasmato etch the exposed portion and the remaining photoresist protects thesubstrate regions which it covers. The photoresist layer is removed fromthe etched substrate using a stripper to complete the pattern onto thesubstrate surface.

The following examples further illustrate the present invention.

EXAMPLE 1

A photoresist composition including 6.43 wt. % of a photosensitivechemical, 19.47 wt. % of a polymer resin, 70.4 wt. % of 3-methoxybutylacetate, and 3.70 wt. % of 4-butylolactone was drop-wise applied to 4inch bare glass plates and the glass plates were then rotated at aconstant rate. The resulting glass plates were heat-dried at 135° C. for90 seconds to obtain a photoresist film layer with a thickness of 1.60 μon the glass. The resulting glass plates were exposed to ultravioletlight using a mask and then dipped into a 2.38% tetramethyl ammoniumhydroxide (TMAH) aqueous solution for 75 seconds to remove the exposedportions and obtain photoresist patterns.

It was found that the photoresist composition had a goodphotosensitivity. Furthermore, since the thickness is linearly increasedaccording to the increases in the spin speed, layer thickness can beeffectively predicted if the spin speed is changed.

The positive type photoresist composition of the present invention hasincreased photosensitivity and rendered a good remainder ratio andthickness of layer so that the composition can be easily applied tovarious industrial applications. Furthermore, the composition has nounpleasant odor so that it can contribute to a favorable workenvironment.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

What is claimed is:
 1. A composition for positive photoresist,comprising: a polymer resin for forming a photoresist layer; aphotosensitive chemical that changes solubility of the photoresist layerwhen exposed to some form of radiation; and 3-methoxybutyl acetate, and4-butyrolactone as a solvent, wherein the ratio of 3-methoxybutylacetate:4-butyrolactone is 60 to 80 parts by weight 3-methoxybutylacetate: 2 to 10 parts by weight 4-butyrolactone.
 2. The composition ofclaim 1, wherein the polymer resin is a novolak resin and thephotosensitive chemical is a diazide-based compound.
 3. The compositionof claim 1, wherein the photoresist composition includes 10 to 25 wt. %of polymer resin, 4 to 10 wt. % of photosensitive compound, and 65 to 85wt. % of solvent.